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Search: id:A033568
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| A033568 |
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Second pentagonal numbers with odd index: (2*n-1)*(3*n-1). |
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+0
7
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| 1, 2, 15, 40, 77, 126, 187, 260, 345, 442, 551, 672, 805, 950, 1107, 1276, 1457, 1650, 1855, 2072, 2301, 2542, 2795, 3060, 3337, 3626, 3927, 4240, 4565, 4902, 5251, 5612, 5985, 6370, 6767, 7176, 7597
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OFFSET
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0,2
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FORMULA
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G.f.: A(x) = (1-x+12*x^2)/(1-x)^3.
a(n)=12*n+a(n-1)-23 (with a(1)=1) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 15 2009]
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EXAMPLE
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For n=2, a(2)=12*2+1-23=2; n=3, a(3)=12*3+2-23=15; n=4, a(4)=12*4+15-23=40 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 15 2009]
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CROSSREFS
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Cf. A005449, A049453, A033570.
Sequence in context: A007217 A070009 A070170 this_sequence A032016 A001007 A152015
Adjacent sequences: A033565 A033566 A033567 this_sequence A033569 A033570 A033571
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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